linux-kernel - Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom

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Date:   Thu, 20 Aug 2020 23:18:40 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>, timmurray@...gle.com,
        mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
        esyr@...hat.com, christian@...lner.me, areber@...hat.com,
        shakeelb@...gle.com, cyphar@...har.com, oleg@...hat.com,
        adobriyan@...il.com, akpm@...ux-foundation.org,
        gladkov.alexey@...il.com, walken@...gle.com,
        daniel.m.jordan@...cle.com, avagin@...il.com,
        bernd.edlinger@...mail.de, john.johansen@...onical.com,
        laoar.shao@...il.com, minchan@...nel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in
 __set_oom_adj when not necessary

On 2020/08/20 23:00, Christian Brauner wrote:
> On Thu, Aug 20, 2020 at 10:48:43PM +0900, Tetsuo Handa wrote:
>> On 2020/08/20 22:34, Christian Brauner wrote:
>>> On Thu, Aug 20, 2020 at 03:26:31PM +0200, Michal Hocko wrote:
>>>> If you can handle vfork by other means then I am all for it. There were
>>>> no patches in that regard proposed yet. Maybe it will turn out simpler
>>>> then the heavy lifting we have to do in the oom specific code.
>>>
>>> Eric's not wrong. I fiddled with this too this morning but since
>>> oom_score_adj is fiddled with in a bunch of places this seemed way more
>>> code churn then what's proposed here.
>>
>> I prefer simply reverting commit 44a70adec910d692 ("mm, oom_adj: make sure
>> processes sharing mm have same view of oom_score_adj").
>>
>>   https://lore.kernel.org/patchwork/patch/1037208/
> 
> I guess this is a can of worms but just or the sake of getting more
> background: the question seems to be whether the oom adj score is a
> property of the task/thread-group or a property of the mm. I always
> thought the oom score is a property of the task/thread-group and not the
> mm which is also why it lives in struct signal_struct and not in struct
> mm_struct. But
> 
> 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj")
> 
> reads like it is supposed to be a property of the mm or at least the
> change makes it so.

Yes, 44a70adec910 is trying to go towards changing from a property of the task/thread-group
to a property of mm. But I don't think we need to do it at the cost of "__set_oom_adj() latency
Yong-Taek Lee and Tim Murray have reported" and "complicity for supporting
vfork() => __set_oom_adj() => execve() sequence".